Losing mature common bristlenose

Hi,
Hope I have covered all the points here - used a different template. I can redo if necessary.
I am at a complete loss. No idea what is killing off my long established colony.



1. Water parameters
a) Temperature range. - 25 C
b) pH. 7.3
c) GH. 12
d) KH 6
e)Ammonia 0 , Nitrate 40 , Nitrite 0
f) Water change frequency
twice weekly 10-15% each time


2. Tank set up
a) Size. 2700 litres
b) Substrate. sand
c) Filtration. 4 fx5
d) Furnishings. bogwood, ornaments
e) Other tank mates. filament barbs, clown loaches, synodontis, scissortails, L066, L340 , clown plecs, banjo cat, midnight cats, cories, porthole cats, rainbow cichlids
f) How long has it been set-up? At least a year, probably 2 years
g) When was the last new fish added? 3 months L66
h) Foods used and frequency? twice daily, flake am, catfish pellets, courgette, frozen bloodworm, live river shrimp - harvested from other tank.

3. Symptoms / Problem description
No symptoms until they turn up dead but after losing a couple of 8 years plus bn females I have now lost more of them and am now losing males. Lost both of my alpha males.
Younger fish seem fine. I have had several bloodlines in there over the years.
No other fish are affected.
No changes to the tank at all.
I have new fish in other tanks but so far as I know I have not cross contaminated and bn seem fine.

4. Action taken (if any)
Tested water as above.
Large water changes - hma water. Taken out some of the furniture so bodies more easily found.

5. Medications used (if any)
none


Ideas anyone ? Inbreeding issues. Can't see how anything would be so specific to particular fish. Lost my second alpha male yesterday - he had the best branching bristles, really complex - just like a mature stag.

Alison

It sounds to me that this might be an age problem as if I remember right the average age for a Bristlenose is 5-8 years and it sounds like its your older ones that are going   

 BTW

yeah, sounds like age to me.

8 years is a good innings for a BN.

Sounds like an amazing tank BTW. I'd LOVE to see some pics

I haven't explained it well. It started with the real oldie females but over the past months has wiped out all my mature fish. Many of them will be less than 6. Age doesn't usually act so quickly across all fish.
I was wondering if I somehow introduced something that they were susceptible to. Or could it be some of the other fish as they have matured?
I have seen clown loaches and bn squabbling over holes but nothing more.